1. Field of the Invention
The present invention relates to radio communications systems, and more particularly to extending the upper frequency limit of communications radios or transceivers.
2. Discussion of the Known Art
Typically, radio frequency (RF) transceivers constructed for use in the Joint Tactical Radio System (JTRS) have an upper operating frequency limit of about 2 GHz. This limit is not sufficient to support new and emerging wideband networking waveforms such as, e.g., Communication Data Link (CDL) and IEEE 802.16 WiMAX, however. Such waveforms may require the upper frequency limit of a transceiver to be extended to as high as 6 GHz.
U.S. Pat. No. 6,549,082 (Apr. 15, 2003) describes a high frequency oscillator. A reference oscillator in the form of a digital controlled frequency synthesizer with an external tank circuit, operates in a range of 1.25 to 1.5 GHz. A phase-locked loop circuit of the synthesizer is combined with the reference oscillator in an integrated circuit, preferably using a Bipolar CMOS (BiCMOS) silicon/germanium process. According to the patent, a tuned output range of 5 to 6 GHz may be provided by using a dividing factor of four.
U.S. Pat. No. 7,313,368 (Dec. 25, 2007) discloses a transceiver architecture including a dual-band, single frequency synthesizer for wireless communication in the 2.4 GHz and 5 GHz International industrial, scientific, and medical (ISM) bands. A high frequency integrated circuit down converts a received multi-mode frequency signal, and a base frequency decoding circuit performs the processes of up-sampling and emitting a signal so as to transmit/receive a dual band signal by using the single frequency synthesizer.
Notwithstanding the above, there is a need to extend the upper frequency limit of existing tactical radio systems or transceivers from 2 GHz to 6 GHz so that the systems can support the new and emerging wideband networking waveforms transmitted above 2 GHz in the RF spectrum, while confining the space occupied by the extended systems within an even smaller volume than that allotted for the existing systems.